The present invention is directed to a method and apparatus for dispensing fluids from a pipette, and particularly for dispensing small volumes of liquids from a micropipette. The invention is also directed to a method and apparatus for capturing and dispensing a predetermined volume of a liquid sample containing volatile components using a micropipette.
Chemical analysis often requires transferring samples between vessels or containers and adding various reagents to the samples. In recent years, various devices have been developed for the automation of pipettes for transferring the sample from storage vessels to various reaction containers. Automated pipetting devices are particularly desirable where large numbers of samples are being handled. Automated pipetting devices have the advantage of accurately transferring uniform and consistent volumes of various samples to a desired location.
One analytical device that has gained widespread use in recent years is mass spectrometry. In particular, matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is commonly used in the analysis of analytes and other biological materials. The ionization of biomolecular samples using a MALDI mass spectrometer and particularly time of flight mass spectrometers apply a sample to the surface of a solid support which is then introduced into the vacuum system of the mass spectrometer. The solid support typically contains a large number of samples arranged in an array. The sample support is positioned in the mass spectrometer so that the samples are positioned in the focus point of the laser.
The support plate is loaded with the samples to be analyzed by applying small drops of a solution containing the sample. The solution generally includes a volatile or low boiling solvent or carrier, which evaporates quickly to produce a sample spot. Typically, a matrix substance is added to the solution for the MALDI mass spectrometer analysis. The matrix encapsulates the sample material as the solvent dries. In other methods, a matrix layer is first applied to the support and dried. Thereafter, the sample is then applied onto the dried matrix material. A solvent can be applied to disperse the sample in the matrix.
Automation of the sample loading onto the support plate provides speed and accuracy to the process. In particular, automation enables the analysis of thousands of samples per day that is not available by manually handling of the samples. In addition, higher densities of samples can be loaded onto the MALDI sample plate by automation than can be obtained by manual manipulation of the samples. One example of an automated device for loading samples onto a support for a mass spectrometer is disclosed in U.S. Pat. No. 5,770,860 to Franzen.
Biological samples are often stored and processed in micro-titer plates having a large number of wells. Each sample well of the micro-titer plate contains a sample to be analyzed. Micro-titer plates generally have at least 96 sample wells arranged in a grid. Micro-titer plates having 384 wells and 1536 wells are also known.
MALDI mass spectrometry often forms the samples on a support using a volatile solvent, which can evaporate quickly. When a pipette is used to transfer the sample from a storage vial to the support plate, an amount of the sample is drawn into the pipette and the pipette is moved to a location above the support plate. A disadvantage of this pipetting method is that droplets of the liquid sample collect on the outer surface of the pipette. In addition, the, liquid sample is drawn from the inside of the pipette up along the outer surface by the surface tension of the liquid sample. The evaporation of the volatile solvent interferes with the ability to dispense predetermined amounts of the solvent from the pipette into the plate. In some instances, the volatile solvents can evaporate from the liquid and form crystals on the outside of the pipette. The buildup of the dried sample and matrix material on the outer surface of the pipette can interfere with dispensing of the sample onto the support plate and can result in cross contamination of samples as the pipette is transferred between sample wells.
Although the prior methods have been suitable for their intended purpose, they have certain disadvantages due to the nature of the solvent and carrier systems and the support plates. Accordingly, there is a continuing need in the industry for an improved method for handling biological samples.
The present invention is directed to a method and apparatus for dispensing fluids from a pipette. More particularly, the invention is directed to a method and apparatus for dispensing a predetermined amount of liquid sample using a micropipette where the liquid sample contains a volatile solvent or carrier.
Accordingly, a primary aspect of the invention is to provide a method and apparatus for loading a plurality of samples onto a support for various processes. The method and apparatus are particularly suitable for depositing a sample onto a support plate for mass spectrometry analysis.
Another aspect of the invention is to provide an automated method for transferring a large number of samples from sample containers to a support surface and for producing microarrays for various uses.
Still another aspect of the invention is to provide a method of pipetting a liquid sample containing a volatile solvent or carrier in a manner to minimize evaporation of the solvent from the pipette. Small quantities of volatile liquids can be pipetted with little or no loss of the liquid.
A further aspect of the invention is to provide a method of handling liquid samples that contain a volatile liquid component and transferring a small volume of the sample to a selected location. In one embodiment, the method transfers liquids having a volume of about 10 microliters or less.
Another aspect of the invention is to provide a method of loading a plurality of samples onto a plate for MALDI mass spectrometry, direct ionization mass spectrometry, fast atom bombardment, field desorption, and atmospheric pressure ionization.
Still another aspect of the invention is to provide a method of transferring liquid samples from the wells of a microtiter plate to a support or vessel using a micropipette with minimum evaporation or loss of the liquid and sample between the microtiter plate and the support plate.
A further aspect of the invention is to provide a method for loading liquid samples onto a support plate using a pipette or probe containing a pressure transmitting liquid for drawing a liquid sample into the pipette and dispensing the liquid sample onto the support plate.
Another aspect of the invention is to provide a method for transferring a liquid sample using a pipette containing a pressure transmitting liquid where the sample liquid is drawn into the pipette to form a bubble or volume of the liquid sample that is spaced from the end of the pipette a distance to reduce evaporation and loss of the liquid sample from the pipette.
A still further aspect of the invention is to provide a method of transporting a liquid sample using a pipette and inhibiting the formation and evaporation of droplets of the liquid sample on the outer surface of the pipette.
Another aspect of the invention is to provide a method of transporting a liquid sample in a pipette by forming an air pocket on the upstream side of a volume of the liquid sample and a volume of a barrier material on the downstream side of the volume of the liquid sample between the liquid sample and the discharge end of the pipette.
A further aspect of the invention is to provide a method of transporting a liquid sample in a pipette, where an air pocket is positioned above the liquid sample and an air pocket is provided between the liquid sample and the end of the pipette, and where the sample is discharged from the pipette with sufficient force to dispense and deposit the sample on a support plate substantially without the liquid adhering to the pipette.
The aspects of the invention are basically attained by providing a method of depositing a liquid sample onto a support. The method comprises the steps of: providing a support having a top surface for supporting a liquid sample and providing a pipette having an axial passage and an open axial end. A volume of a liquid sample is drawn through the open axial end of the pipette into the axial passage. A volume of a barrier material is drawn through the open axial end of the pipette to draw the volume of the liquid sample into the axial passage and to space the liquid sample from the axial end by the volume of the barrier material to inhibit evaporation of the liquid sample from the pipette. The pipette is positioned above a target site on the support to expel the volume of the barrier material from the pipette, and discharge the liquid sample onto the target site.
The aspects of the invention are further attained by providing a method of loading at least one biological material onto a mass spectrometer plate. The method comprises the steps of: drawing a volume of a liquid sample and drawing a volume of a barrier material into a pipette to space the volume of liquid from an outlet end of said pipette to inhibit loss of said liquid material from the pipette. The pipette is positioned over a mass spectrometer plate while retaining the volume of liquid sample completely within the pipette. The barrier material and the volume of liquid sample are discharged and the liquid sample is deposited onto a target site on the plate.
The aspects of the invention are also attained by providing a method of loading a sample onto a mass spectrometer plate. The method comprises the steps of: providing a pipette having an axial passage and an open axial end; inserting the open axial end of the pipette into a sample supply; and drawing a volume of the liquid sample into the axial passage. The open end of the pipette is removed from the liquid sample and a volume of a barrier material is drawn into the pipette through the open axial end to space the volume of liquid sample from the open axial end to inhibit evaporation of the sample. The open axial end of the pipette is positioned over a target site of a mass spectrometer plate and the barrier material and volume of liquid sample is discharged from the pipette to load the volume of liquid sample on the target site.
The aspects of the invention are further attained by providing a method of forming a sample spot on a mass spectrometer plate suitable for mass spectrometer analysis. The method comprises the steps of: loading a liquid sample containing an analyte to be analyzed onto a support plate to form a liquid sample spot and pipetting a liquid matrix forming material directly onto the sample spot. The liquid contains a volatile liquid having a vapor pressure of at least 3.5 kPa at 25xc2x0 C. and a mass spectrometry matrix material. The volatile liquid is evaporated to recrystallize the matrix material and analyte.
The various aspects, advantages and other salient features of the invention will become apparent to one skilled in the art in view of the following detailed description of the invention and the annexed drawings which form a part of this original disclosure.